Towards a predictive understanding of how mycorrhizal types influence the decomposition of soil organic matter
Final Report Abstract
Forests store huge amounts of terrestrial carbon (C) and remove billion of tons of anthropogenic C from the atmosphere by photosynthesis every year. About half of the assimilated C is allocated to roots and root symbionts such as mycorrhizal fungi. Nearly all fine roots of trees are colonized by either arbuscular (AM) or ectomycorrhizal (ECM) fungi. In contrast to most other soil microorganisms, mycorrhizal fungi are not limited in C as they are fueled with C from their autotrophic host. Hence, they not only act as important C sink in soils, but also have the potential to play a major role in nutrient mobilization through soil organic matter (SOM) decomposition. This project aimed to investigate the role of mycorrhizal types for C input to the soil, SOM cycling and C storage. To achieve this aim, we applied innovative tools (isotope approaches coupled with microbiological techniques) and conducted studies on various temporal and spatial scales. Our results showed a 2-5 times higher C input and greater rhizosphere extension of plants with ECM. Moreover, since ECM fungi are not limited in C the activity of enzymes involved in C cycling decreased while the activity of nitrogen (N) and phosphorus (P) cycling enzymes increased. The symbiosis with AM fungi decreased the relative C allocation (% of total assimilated C) to roots but in turn increased the net rhizodeposition. Although net rhizodeposition was higher for mycorrhizal plants 16 weeks after transplanting, the rhizosphere priming effect was comparatively lower. This indicates a higher potential for C sequestration by plants colonized with AM fungi. In forest plots dominated by ECM trees, with low mineral N availability and a lot of SOM in particulate form, SOM decomposition increased by 58% under the influence of an invasive gras. In contrast, in plots dominated by AM trees, characterized by high N availability and most SOM in mineral-associated forms, decomposition decreased by 14%. These results demonstrate that despite higher total C stocks in the topsoil of ECM dominated plots, the C is less stabilized. The contribution of various sources to particulate and mineralassociated organic matter was investigated in a second field study. As a prerequisite we developed a method to extract AM hyphae from roots for isotope analysis. Our results from the field experiment suggest fungal, not plant residues, as the main source of the mineral-associated C pool. This result was confirmed by amino sugar analysis, as biomarkers of fungal and bacterial necromass. Fungal residues (ECM and saprotrophic fungi) contribute more than 60% to the mineral-associated organic matter irrespective of the tree species. The present project contributed to a more comprehensive understanding on the role of distinct mycorrhizal types on C input, SOM decomposition and nutrient cycling, as well as the contribution of various sources to SOM fractions in forest systems dominated by trees with AM and ECM association.
Publications
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Arbuscular mycorrhiza enhances rhizodeposition and reduces the rhizosphere priming effect on the decomposition of soil organic matter. Soil Biology and Biochemistry, 140, 107641.
Zhou, Jie; Zang, Huadong; Loeppmann, Sebastian; Gube, Matthias; Kuzyakov, Yakov & Pausch, Johanna
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Organic matter priming by invasive plants depends on dominant mycorrhizal association. Soil Biology and Biochemistry, 140, 107645.
Kumar, Amit; Phillips, Richard P.; Scheibe, Andrea; Klink, Saskia & Pausch, Johanna
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Stable C and N isotope natural abundances of intraradical hyphae of arbuscular mycorrhizal fungi. Mycorrhiza, 30(6), 773-780.
Klink, Saskia; Giesemann, Philipp; Hubmann, Timo & Pausch, Johanna
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Ectomycorrhizal and non‐mycorrhizal rhizosphere fungi increase root‐derived C input to soil and modify enzyme activities: A 14C pulse labelling of Picea abies seedlings. Plant, Cell & Environment, 45(10), 3122-3133.
Zhou, Jie; Gube, Matthias; Holz, Maire; Song, Bin; Shan, Immo; Shi, Lingling; Kuzyakov, Yakov; Dippold, Michaela A. & Pausch, Johanna
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Stable isotopes reveal that fungal residues contribute more to mineral-associated organic matter pools than plant residues. Soil Biology and Biochemistry, 168, 108634.
Klink, Saskia; Keller, Adrienne B.; Wild, Andreas J.; Baumert, Vera L.; Gube, Matthias; Lehndorff, Eva; Meyer, Nele; Mueller, Carsten W.; Phillips, Richard P. & Pausch, Johanna
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Tracing soil carbon and nitrogen cycling in arbuscular and ectomycorrhizal systems. Dissertation, 2022, University of Bayreuth, Faculty of Biology, Chemistry, Earth Sciences.
Klink S.
